Example embodiments of inventive concepts relate to voltage monitors.
In a semiconductor circuit, particularly a high-performance semiconductor circuit, a supplied voltage may swing depending on an operation environment and the level of a performed operation within the circuit. Generally, a voltage supplied to support the worst case when a voltage decreases significantly is set to be greater than a value required for the case of a normal state. However, because this conventional method causes power consumption of a semiconductor circuit to increase, competitiveness of products is weakened.
To overcome the above disadvantage, when a supplied voltage of a circuit starts decreasing, the decrease of the supplied voltage is detected. Operating speed or work level of the circuit is changed based on a result of the detection to allow a normal operation to be performed even when a voltage decreases. For achieving this, it is important to rapidly and accurately know a voltage state of the circuit. A manner of monitoring a voltage of a semiconductor circuit is classified into a digital manner and an analog manner. Since it is difficult to perform integration into a digital circuit and perform a high-speed operation in the analog manner, the digital manner has been widely used in a high-speed digital circuit.